Stefano D’Errico,Raffaele LaRussa,Aniello Maiese,Alessandro Santurro,Matteo Scopetti,Silvia Romano,Martina Zanon,Paola Frati3,,Vittorio Fineschi3,,

1.Department of Medical,Surgical and Health Sciences,University of Trieste,Trieste,Italy;2.Department of Clinical and Experimental Medicine,University of Foggia,Foggia,Italy;3.IRCSS Neuromed Mediterranean Neurological Institute,Pozzilli,Italy;4.Department of Surgical Pathology,Medical,Molecular and Critical Area,University of Pisa,Pisa,Italy;5.Department of Anatomical,Histological,Forensic and Orthopaedic Sciences,Sapienza University of Rome,Rome,Italy

ABSTRACT Oxidative stress is considered the principal mediator of myocardial injury under pathological conditions.It is well known that reactive oxygen (ROS) or nitrogen species (RNS) are involved in myocardial injury and repair at the same time and that cellular damage is generally due to an unbalance between generation and elimination of the free radicals due to an inadequate mechanism of antioxidant defense or to an increase in ROS and RNS.Major adverse cardiovascular events are often associated with drugs with associated findings such as fibrosis or inflammation of the myocardium.Despite efforts in the preclinical phase of the development of drugs,cardiotoxicity still remains a great concern.Cardiac toxicity due to second-generation antipsychotics (clozapine,olanzapine,quetiapine) has been observed in preclinical studies and described in patients affected with mental disorders.A role of oxidative stress has been hypothesized but more evidence is needed to confirm a causal relationship.A better knowledge of cardiotoxicity mechanisms should address in the future to establish the right dose and length of treatment without impacting the physical health of the patients.

Second-generation (atypical) antipsychotics are used in the treatment of mental disorders (schizophrenia,bipolar disorder,major depressive disorder).Since marketed,clozapine was widely used because of its efficacy in drugresistant schizophrenia and freedom from extrapyramidal effects.After clozapine,other antipsychotics were introduced (olanzapine,quetiapine,risperidone)with similar effects and the same safer profile and soon became the mainstay of the treatment of schizophrenia.[1]The therapeutic effect of secondgeneration antipsychotic agents is related to dopaminergic D2 receptor antagonism and to the blockage of serotonin receptors.Major cardiovascular adverse effects (tachycardia,bradycardia,hypertension,hypotension,syncopal episodes) and electrocardiographic abnormalities (prolonged QT interval)are reported in patients suffering from mental disorders and treated with antipsychotics.[2–8]An increased risk of sudden death has been also reported but the risk of underreporting is concrete because of the lack of a systematic post-mortem examination.[9–13]In addition,individuals with schizophrenia are known to be at greater risk of cardiac death,in part linked to inadequate lifestyles that predispose to cardiovascular disease,in part due to poor compliance with health care.[14–16]However,many typical and atypical antipsychotic drugs have been reported in the literature to significantly increase the risk of sudden cardiac death in patients with psychiatric disorders,[17]and this has led to restrictions in clinical practice or the withdrawal of these molecules from the market.A retrospective cohort study showed that the incidence of sudden cardiac death in subjects taking antipsychotics is increased (dose-related increase) compared to non-users of antipsychotics,regardless of the pharmacological class.[18]

Sudden antipsychotic cardiac death appears to be linked to arrhythmic mechanisms,dilated heart disease,and myocarditis.[19–21]In the pathogenesis of the aforementioned cardiological alterations,an involvement of oxidative stress has been suggested,with an increase in reactive oxygen (ROS).[22]ROS modulates multiple cellular signaling pathways in physiological conditions.However,when the production of intracellular ROS is excessive it causes damage to the molecular components of the cell,favoring the pathogenesis of various diseases with particular reference to cardiovascular ones.

Despite the large use,factors underlying cardiovascular disease in patients treated with antipsychotics are still far to be completely understood and need to be deeply studied.[23–27]Growing interest is aimed at understanding the contribution of antipsychotic therapy in the genesis of cardiac toxicity in schizophrenic patients.

The purpose of the present study is to review the scientific literature on the topic and propose a possible explanation of antipsychotics-related cardiotoxicity.

LITERATURE ANALYSIS

Relevant scientific articles were identified from PubMed,Cochrane Central,Scopus,Web of Science,Science Direct,EMBASE up to January 2020 using the following keywords:“atypical antipsychotics”,“cardiomyopathy”,“myocarditis”,“oxidative stress”,and“sudden cardiac death”.The main keywords were individually searched in association with each of the others.

The resulting 527 references were screened to exclude duplicates,which left 67 articles for further consideration.In addition,non-English papers were excluded and the following inclusion criteria were used:original research articles,reviews and minireviews,documents and guidelines promulgated by scientific societies and international organizations,and book chapters.

The papers not suitable for the review were excluded,a hand search was performed through the reference lists of the included articles.These publications were carefully evaluated considering the main aims of the review.An excel data extraction form was used to extract pivotal data,including publication year,first author,types of scientific articles,the topic of the study.This evaluation left 106 scientific papers,distributed as original research articles,reviews,and mini-reviews (Figure 1).These reports were published between 1981 and 2020.

Figure 1 Relevant scientific articles were identified from PubMed,Cochrane Central,Scopus,Web of Science,Science Direct,EMBASE up to January 2020 using the following keywords:“atypical antipsychotics”,“cardiomyopathy”,“myocarditis”,“oxidative stress","sudden cardiac death". The main keywords were individually searched in association with each of the others.The resulting 527 references were screened to exclude duplicates,which left 67 articles for further consideration.In addition,non-English papers were excluded and the following inclusion criteria were used:original research articles,reviews and mini-reviews,documents and guidelines promulgated by scientific societies and international organizations,and book chapters.

The features of included papers were described in Tables 1–3.The table was organized by dividing the main topics of the present review into three subgroups:the relationship between heart disease and use of antipsychotic drugs,the relationship between cardiovascular pathologies and oxidative stress,and the relationship between antipsychotics and cardiac oxidative stress.In each subgroup,the type of scientific article,the methods used and the purpose of the work were indicated.

Table 1 Baseline characteristics of the studies with the correlation between use of antipsychotics and heart disease.

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Table 2 Baseline characteristics of the studies with the correlation between use of antipsychotics and oxidative stress.

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Table 3 Baseline characteristics of the studies with the correlation between oxidative stress and heart disease.

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Oxidative Stress and Cardiac Injury

Superoxide anion (O2-),hydroxyl radical (OH-),hydrogen peroxide (H2O2),singlet oxygen,carboncentered radicals,peroxynitrite (ONOO-),nitric oxide(NO),and nitrogen dioxide radicals are the free radicals identified in the human heart.Under basal conditions,the production of free radicals is low.However,the maintenance of intracellular redox homeostasis is fundamental to guarantee the physiological cardiac functions (development and maturation of cardiomyocytes,the release of intracellular calcium,and the coupling of cardiac excitation/contraction).[28]The physiological intracellular levels of ROS are maintained by an antioxidant defense system which includes superoxide dismutases,catalase,the glutathione peroxidase/reductase system,and the peroxiredoxin/thioredoxin system.When pathological conditions occur (e.g.,myocardial ischemia),hyperproduction of O2-is observed from multiple cellular sources,the cellular antioxidant defense system is depleted and the free radicals scavenging enzyme system superoxide dismutase,glutathione peroxidase,chloramphenicol acetyltransferase is significantly reduced.[29]ROS can cause severe oxidative damage,especially to DNA,lipids,and proteins.Lipids are the class of biological molecules most susceptible to attack by oxygen free radicals.Oxidation takes place on the fatty acids present in cell membranes or lipoproteins,producing toxic substances for cells and tissues.Furthermore,as far as proteins are concerned,these,following the oxidation of the–SH groups of some amino acids (His,Arg,Lys,Pro) and the liberation of iron by the degradation of the porphyrin rings by ROS,lose their physiological structure and therefore functionality.In DNA,the oxidative phenomena concern the purine and pyrimidine bases;[30]one of the most studied markers of DNA damage from oxidative damage is represented by 8-OHdG.[31]The excessive production of ROS determines the activation of cell death,with consequent apoptosis or myocardial necrosis.[32]In the pathogenesis of cardiac pathologies,a fundamental role is played by mitochondrial-derived ROS,which derives from electron transfer into the mitochondrial respiratory chain complexes and from the action of mitochondrial proteins.Mitochondria are one of the main drivers of intracellular oxidant production and other relevant sources are nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOX family of enzymes).Besides,other enzymes contribute to intracellular ROS production,including xanthine oxidase,nitric oxide synthase (NOS),cyclooxygenases,cytochrome P450 enzymes,and lipoxygenases.

Several data in the literature suggest that this type of ROS is involved in the pathogenesis of numerous cardiac pathologies,such as myocardial infarction,heart failure,and diabetic cardiomyopathy.[28]Specifically,in cardiac infarction,hypoxia induces a decrease in adenosine triphosphate (ATP) with consequent loss of depolarization of the mitochondrial membrane with activation of anaerobic glycolysis,lactate formation,and cytosolic calcium accumulation.[33]These cellular damages are finally further implemented by the reperfusion of hypoxic cells,causing an increase in cellular necrosis.Otherwise,in heart failure,the cellular modifications related to ROS occur in a more dilated time span.The basis of these modifications is the interaction between the increase in angiotensin II and the increase in myocardial stress,with consequent cardiac remodeling,contractile dysfunction,and the onset of arrhythmias.[34]The role played by NADPH oxidase (NOX) seems to be relevant in the failure,which can uncouple the NO synthase and promote O2-.[35]Also,angiotensin II-mediated ROS increase activates nuclear factor kappaB induced hypertrophy pathway.[32]

Instead,diabetic heart disease is linked to the accumulation of fatty acids in cardiomyocytes with a consequent reduction in the use of carbohydrates as an energy substrate especially during periods of high demand for ATP and,consequently,increased formation of ROS with mitochondrial damage and promotion of apoptosis of cardiomyocytes.The peroxisome proliferator-activated receptor,a nuclear hormone receptor which modulates the metabolism of glucose and fatty acids,is involved in this heart disease.[36]

Finally,oxidative stress,in association with the increase in inflammation products,promotes endothelial dysfunction through the inactivation of NO,an important molecule with a vasodilator and anti-atherogenic role.NO inactivation is promoted by NADPH oxidase and uncoupled NOS.[37]

In light of these data,there is growing interest in the literature about the role played by ROS in the pathogenesis of cardiovascular diseases and the possible experimental use of antioxidant molecules in the treatment of heart diseases.

Cardiovascular Complications from Antipsychotics

Atypical antipsychotic therapy is notoriously associated with cardiovascular pathologies and an increase in sudden cardiac death.

Second-generation antipsychotic drugs have a significant influence on the development of metabolic syndrome,which is known to be a risk factor for cardiovascular disease.Furthermore,a correlation is known with myocarditis,[8]dilated heart disease,[10]and QT tract prolongation,which represents an important risk factor for the development of malignant arrhythmias and sudden cardiac death.[38]In addition to this,subjects affected by schizophrenia,regardless of the therapy taken,have additional cardiovascular risk factors on a dysmetabolic basis,such as type 2 diabetes mellitus,reduced glucose tolerance,insulin resistance,and obesity.[5]

As for the adverse effects of the dysmetabolic type,as previously mentioned,atypical antipsychotics can cause weight gain,especially olanzapine and clozapine,and related metabolic disorders such as insulin resistance,type 2 diabetes mellitus,dyslipidemia,and diabetic ketoacidosis.[16]

It is also known that obese and diabetic subjects have an increased incidence of atrial fibrillation,ventricular ectopia,and long QT.[39]Besides,diabetes mellitus and obesity are associated with an increased risk of sudden cardiac death,which is often caused by ventricular arrhythmias.As regards the electrocardiographic changes induced by antipsychotics,it has been observed that the use of these drugs is associated with prolongation of the QTc,that is,prolonged cardiac repolarization.[40]QTc is defined on the electrocardiogram as the period between the onset of the Q wave (ventricular depolarization) and the cessation of the T wave (ventricular repolarization) corrected for heart rate.It is known to be an indicator of potential proarrhythmic toxicity as it can lead to a specific polymorphic ventricular arrhythmia known as torsade de pointes which can develop into malignant arrhythmias such as ventricular fibrillation and sudden cardiac death.The most common mechanism of antipsychotic mediated QTc prolongation appears to be blockage of the hERG channel in the myocardium which prevents outward movement of potassium responsible for ventricular depolarization.[41]The risk increases in the presence of underlying heart diseases associated with abnormal repolarization,electrolyte abnormalities,and co-treatment with other drugs (diuretics,antidepressants,mood stabilizers).[42]For this reason,treatment with antipsychotics should only be undertaken if there is a concrete therapeutic advantage and some authors propose the application of stratification measures for patients at greater risk of developing this condition before starting therapy.

Among antipsychotics,there was an increased risk of QTc prolongation for typical antipsychotics;in particular droperidol and thioridazine are associated with an increase in QTc in a dose-dependent manner.[43]However,there are data in the literature that also describe it for atypical antipsychotics.Clinical studies have reported a clear association of the aforementioned electrocardiographic alteration and sertindole and risperidone,in a dose-dependent manner,[42]although among the atypical antipsychotics,ziprasidone is the riskiest,[44]so much so that it has been proposed to take an electrocardiogram at the start of therapy.[45]

Preclinical studies have reported a dose-dependent prolongation of the QT interval with other atypical antipsychotics as well,namely clozapine and olanzapine.[42]Finally,antipsychotic therapy,although rarely,can be associated with severe complications such as myocarditis and evolving cardiomyopathies towards decompensation.This is especially true of clozapine,[45]an atypical antipsychotic used for resistant schizophrenia and prevention of suicide risk.[46]In addition to myocarditis,cases of cardiomyopathy have been described,albeit more rarely.[47]This is also more frequent with clozapine with a later onset than myocarditis (the average onset was reported in a study after 12 months) and associated with high mortality.[48]Specifically,clozapine,in therapeutic doses,can also be associated with the occurrence of serious cardiovascular side effects,very rare but described in the literature as dilated cardiomyopathy,pericarditis and concomitant myopericarditis associated with parenchymal lung disease.[49]Finally,complete atrioventricular blockage by ingestion of massive drug doses of clozapine has been described,[50]which can be fatal if not promptly recognized and managed.

For this reason,the United States Food and Drug Administration has included potentially fatal events and cautious use of clozapine in patients with preexisting cardiac diseases and with severe cardiac conditions among the adverse effects of clozapine.[11]

A retrospective study of all adverse drug reactions reported voluntarily to the Australian Adverse Drug,identified an incidence of suspected myocarditis ranging between 0.7% and 1.2% of patients treated with clozapine,with an average age of 30 years;the disease developed on average two weeks after starting therapy with a mortality rate of 10.3%.[51]

Myocarditis is an uncommon,dose-independent,potentially lethal adverse effect;probably underestimated due to the often,atypical clinical manifestation and the poor compliance of these patients with medical treatment.In fact,the clinical presentation can be very variable,ranging from subclinical forms to fulminant heart failure.

Sudden death after clozapine intoxication due to eosinophilic myocarditis was first described in 1992,[52]but the same was also reported in subsequent several clinical cases with the use of therapeutic doses of the drug.[53]

Although with extremely rare incidence,cardiomyopathy has also been described with quetiapine,an atypical antipsychotic structurally similar to clozapine,suggesting a pharmacological class effect.[54]According to the WHO’s program for international drug monitoring,myocarditis and cardiomyopathy induced by the use of quetiapine are typically present mimicking myocardial infarction with acute ST-segment elevation on electrocardiogram.As well as for clozapine,the mechanism of quetiapine-induced cardiotoxicity is still undefined.

The use of antipsychotics is burdened by an increased risk of sudden cardiac death;in fact,in subjects taking antipsychotics,the risk of sudden cardiac death has more than doubled in consideration also of weight gain,dyslipidemia,and type 2 diabetes mellitus related to antipsychotic treatment.[15]To these risk factors,additional environmental cardiovascular risk factors are added,such as smoking,alcohol abuse,poor diet,a sedentary lifestyle,and stress,which are often present in individuals suffering from schizophrenia.

Sudden cardiac death in patients taking antipsychotics has a multifactorial nature,resulting from a complex interaction between the aforementioned environmental factors,any pre-existing cardiac substrates,both structural and genetic,and the pathological action of these drugs at the cardiac level.However,the underlying molecular mechanisms are still to be understood also concerning the causal weight of a possible heritable component that can make individuals taking antipsychotics more susceptible to sudden cardiac death.

OXIDATIVE STRESS IN ANTIPSYCHOTICRELATED CARDIOMYOPATHIES

Marketed drugs have been often associated with cardiovascular major adverse events and safety concerns due to a significantly increased risk of cardiac fibrosis,myocardial infarction,and myocardial inflammation.Despite efforts in the preclinical phase of the development of drugs,cardiotoxicity remains a great concern due to the lack of sufficient knowledge of the mechanism of cardiotoxicity.Linkage with the entity of intracellular ROS and RNS reaction has been evocated to explain drug-induced myocardial injury.[55]Oxidative and nitrative modifications of key mitochondrial proteins have a central role in drug-induced cardiotoxicity.[56]The oxidative stress resulting from increased free radical generation in cardiomyocytes produces an energetic imbalance,impairment of mitochondrial function,activation of stress-related signaling pathways,p53 accumulation,and cellular loss.[57]By the way,it has been supposed that administration of antioxidants(vitamin C and vitamin E,carvedilol,L-carnitine,N-acetylcysteine,coenzyme Q10,dexrazoxane) is associated with a decrease in ROS-induced cardiomyocytes damage and can play a role in reducing drug-induced cardiotoxicity.[58,59]

An analysis of the literature highlights the need to acquire more data on the pathogenesis of heart disease induced by atypical antipsychotics through post-mortem studies.Conversely,numerous preclinical studies on animal models have been carried out to understand the pathogenesis of heart disease associated with individual antipsychotics.To clarify the role played by oxidative stress in the origin of pathologies affecting the heart induced by atypical antipsychotic drugs,it appears useful to analyze the cardiac pictures related to them individually (Figure 2).

Figure 2 Antipsychotic drugs appear to be linked to arrhythmic mechanisms,dilated heart disease,and myocarditis. In the pathogenesis of the aforementioned cardiological alterations,an involvement of oxidative stress has been suggested,with an increase in reactive oxygen and nitrogen species.

Myocarditis

Myocarditis is mainly described in patients taking clozapine,although it has also been reported in association with the use of other second-generation antipsychotics.

Clear evidence about dose-related clozapine cardiotoxicity is still far to be demonstrated.The mechanism by which clozapine induces cardiotoxicity remains unclear but numerous hypotheses have been proposed.An immunoglobulin E-mediated hypersensitivity (type I allergy) has been proposed for the first time by Killian,et al.[60]as a mechanism of cardiac toxicity in clozapine-treated patients.The results of necropsy showed mainly lymphocytic and mixed infiltrates with myocytolysis,consistent with an acute pharmacological reaction.[61]Then,eosinophilic myocarditis was described in the sudden death of patients treated with clozapine,and a hypereosinophilic action of clozapine was proposed as the main mechanism of cardiotoxicity.[13,20,62,63]Finally,a role of pro-inflammatory cytokines,catecholamines,and oxidative stress was proposed.[64–66]Bioactivation of clozapine in the myocardial tissues is associated with the generation of a chemically reactive nitronium ion metabolite which stimulates cellular injury,lipid peroxidation,and formation of free radical.When bound with a protein of the myocardium,this nitronium ion produces an antigenic complex that stimulates an immune response,and activates macrophages releasing proinflammatory cytokines.[67,68]

To support the importance of oxidative stress in clozapine-associated myocarditis,there is a study conducted by Abdel-Wahab,et al.[69]This study aimed to study the protective effect of captopril against clozapine-induced myocarditis in rats and the possible mechanisms underlying this effect.Administration of the angiotensin converting enzyme inhibitor reduced the histological signs and biochemical markers (creatine phosphokinase–MP isoenzyme and lactate dehydrogenase) of myocarditis,as well as reduced the oxidative stress parameters(NO and DNA degradation products) in a dosedependent manner,suggesting how the cardiointerpretive effect exerted by captopril,in the presence of clozapine-induced myocarditis,is also mediated by the reduction of oxidative stress.

A clinical study reported that the erythrocyte concentration of selenium,an antioxidant molecule,was reduced in schizophrenic patients taking clozapine compared to those who did not take it and compared to patients with mood disorders and healthy controls.This evidence suggests that reduced antioxidant activity may contribute to the development of cardiological complications related to clozapine,including myocarditis.[70]

High levels of tumor necrosis factor-alpha (TNF-α)in association with an increase in catecholamines have also been described in antipsychotic-related myocarditis and dose dependence has been demonstrated.TNF-α hyperproduction is related to the attraction of leukocytes and the generation of further free radicals and cytotoxic proteins.[71–76]High levels of myeloperoxidase were observed in experimental studies with clozapine-treated animals and were indicated as a sensitive marker of neutrophil migration and myocardial injury.[74]Histopathological examination of the heart of mice treated with clozapine showed a significant dose-related increase in myocardial inflammation.The latter correlated with plasma catecholamine and TNF-α levels.Furthermore,this effect was significantly reduced in mice treated with propranolol,compared to controls,suggesting a potential immune-mediated mechanism of action of clozapine.[64]

A preclinical study was conducted to investigate the influence of clozapine,ziprasidone,and sertindole on rat heart morphology and determine whether redox status plays a role in the development of cardiac histopathological changes induced by antipsychotic.[67]The results showed that all three drugs induced cardiac histopathological changes related to a picture of toxic myocarditis.In particular,clozapine increased the activity of superoxide dismutase 1 while ziprasidone reduced the activity of glutathione reductase.Sertindole did not exert any marked effect on the function of antioxidant enzymes in the heart even though myocardial degeneration was observed.In conclusion,treatment with clozapine or ziprasidone induced pathophysiological changes in the rat heart,which seemed to be associated with disturbances in antioxidant capacity.Finally,an antioxidant molecule (edaravone) is effective in reducing myocardial damage in animal models of acute autoimmune myocarditis in association with a reduced state of oxidative stress.[77]

Cardiomyopathy and Cardiac Injury

Heart disease is another adverse effect associated with antipsychotics,although the pathophysiological mechanisms underlying the processes of myocardial remodeling in association with a proarrhythmic condition with increased risk of sudden death are not clear in this context too.

A preclinical study supports the importance of mitochondrial oxidative stress in the presence of heart disease characterized by an increase in angiotensin II levels,proposing the use of mitochondrial antioxidants in the prevention of evolving arrhythmias towards sudden cardiac death in the presence of the renin-angiotensin axis.[78]An increasing amount of data in the literature indicate that cardiac mitochondria are involved in the genesis of arrhythmia.In fact,the energetic state of the mitochondrial network can alter the potassium flows through the ATP-sensitive potassium channels (essential for cell survival in the face of oxidative stress),creating the electrical conditions to favor fatal arrhythmias.For this reason,the cardiac mitochondrial network has emerged as a key target for strategies that seek to reduce arrhythmias through the maintenance of mitochondrial integrity in the face of metabolic stress,preserving the integrity of the membrane potential.

Preclinical data also clearly show that edaravone,a new free radical scavenger,improves the evolution of dilated cardiomyopathy and cardiac remodeling by modulating oxidative stress.[79]

Cardiomyopathy related to taking atypical antipsychotics can,at least in part,be due to cardiomyocyte apoptosis,known to be important in the pathogenesis of patients with severe heart failure from various etiologies.[80]Experimental studies on mice proposed a programmed cell necrotic death(necroptosis) as a possible explanation for the cardiotoxicity of quetiapine.Myocytes treated with quetiapine showed disruption of the cellular membrane,mitochondria swelling with reticulum expansion and generation of oxygen reactive species.These effects are reversed by the administration of necrostatin-1,a TNF inhibitor,[27,81]suggesting a close correlation between inflammation,oxidative stress,and cell death.

Treatment with clozapine has been also associated with an increased cardiac level of total nitrite,a stable end product,an indirect marker of NO.Increased formation of NO produced by inducible NOS has a negative inotropic effect and contributes to the progression of myocardial damage potentially leading to cardiac fibrosis.[82–91]Besides,hyperexpression of peroxynitrite in cardiac samples was observed at an immunohistochemical study which was involved in direct oxidative damage to lipids,proteins,cardiac cells,and myocytes and in the nitration of tyrosine residues of pro-apoptotic proteins in cardiomyocytes.[92,93]In fact,increased NO formation is associated with lipid peroxidation,inactivation of enzymes,and depletion of reduced glutathione and it confirmed that antipsychotic cardiotoxicity is related to increased oxidative stress and weakened antioxidant defense.[94,95]

Metabolic Syndrome

The use of atypical antipsychotics is associated with the development of the metabolic syndrome.It has been proposed that the metabolic alterations induced by these molecules and the increase in arrhythmic risk related to lipid accumulation in cardiomyocytes involve oxidative stress.[96]Cardiac lipid accumulation gives rise to non-ischemic cardiomyopathy called lipotoxic cardiomyopathy.

A preclinical study used a transgenic mouse model of cardiac lipid overload with cardiac overexpression specific to the peroxisome proliferatoractivated receptor gamma,a paradigm of metabolic syndrome in humans.[97]Lipotoxic cardiomyocytes have been shown to exhibit increased ROS production and impaired calcium homeostasis with increased ventricular ectopy.This arrhythmic effect is improved by the inhibition of mitochondrial ROS through the use of a mitochondrial antioxidant molecule suggesting a potential role of mitochondrial antioxidants in the prevention of arrhythmia and sudden cardiac death in obesity and diabetes mellitus.

The role of metabolic stress concerning oxidative stress in the development of these cardiomyopathies is also highlighted in the preclinical study conducted by Gong,et al.[98]Here it was shown that the knockout mice of BAX transmembrane inhibitor motif-containing 1,a suppressor of BAX-mediated cell death and associated with the regulation of ROS,present promotion of metabolic disorders and cardiac dysfunctions induced by the diet rich in fats with increased proinflammatory cytokines and oxidative damage.

In the light of these data,a clear relationship seems to emerge between metabolic/inflammatory alterations and oxidative stress,key elements for the development of structural and arrhythmogenic heart diseases that can lead to fulminant fatal events.

Sudden Cardiac Death

As for sudden cardiac death linked to antipsychotics,this is probably caused by an arrhythmic mechanism,but other mechanisms may be involved,including autonomic effects,inhibition of other ion channels or other acute cardiotoxicities,such as myocarditis associated with the use of clozapine.

In the literature,numerous data are supporting the involvement of oxidative stress in pathological conditions involved in the genesis of sudden cardiac death.

Ventricular arrhythmia is the main cause of sudden cardiac death.A relationship between metabolic disorder and excessive oxidative stress has been proposed with cardiac ion channel dysfunction,which predisposes to ventricular arrhythmias and sudden cardiac death.

ROS production has been hypothesized to play a significant role in arrhythmic substrate production.[99]In particular,an abnormal mitochondrial function can lead to an altered function or expression of the cardiac ion channels responsible for the generation of the cardiac action potential with the possibility of generating re-entry phenomena implicated in the development of malignant arrhythmias.

It is also known that an altered redox state is implicated in cardiovascular pathologies such as atherosclerosis,diabetes mellitus and myocardial ischemia,all conditions that can create a structural substrate for increasing sudden cardiac death.[100]In particular,in myocardial ischemia and heart failure,the efficiency of the mitochondrial electron transport chain is compromised with a consequent increase in ROS production.[101]The aforementioned pathological conditions are notoriously arrhythmogenic and predispose to sudden cardiac death and this could be linked to an altered intracellular electrical and ionic hemostasis consequent to the increase in ROS production.

To support the importance of oxidative stress in the genesis of heart disease associated with sudden cardiac death,some data are emerging from preclinical studies.Doxorubicin (molecule that increases oxidative stress) injection knockout mice for the neuronal nitric oxide synthase-1 adaptive (NOS1AP) protein compared to wild types showed significantly higher mortality,QTc prolongation,and reduced contractile function,as well as the development of spontaneous ventricular tachyarrhythmias.The administration of the antioxidant N-acetyl-L-cysteine significantly reduced the mortality of knockout NOS1AP mice and prevented the prolongation of the QT interval and the reduction of systolic function,suggesting a fundamental role of oxidative stress in the development of ventricular tachyarrhythmias and heart failure,which can cause sudden cardiac death.[102]

POST-MORTEM STUDIES

Several post-mortem studies have been carried out on subjects who used antipsychotics in life to highlight a correlation between the increase in mortality from cardiovascular causes observed on schizophrenics and the use of antipsychotics,typical and atypical (Table 4).

As can be seen in Table 4,epidemiological/observational studies and a cohort study have been carried out to assess cardiovascular risk in subjects taking antipsychotics with a descriptive methodology.[8,18,103–107]In fact,databases were analyzed from hospitals,mainly psychiatric,or from national registers,where the causes of death (cardiac and noncardiac) were reported in the appropriate death certificates.

Table 4 Post-mortem studies carried out on subjects who used antipsychotics in life to highlight a correlation between the increase in mortality from cardiovascular causes observed on schizophrenics and the use of antipsychotics,typical and atypical.

However,in the literature,there are few systematic necropsy studies aimed at analyzing this aspect.The post-mortem investigation described by Kelly,et al.[104]analyzed a sample of sixty-two deceased subjects treated at life with atypical antipsychotics(clozapine and risperidone),highlighting that 11%of the patients treated with clozapine and 7% of those treated with risperidone had died of cardiovascular causes.Also,three cases of cardiomyopathy were described in the group of subjects taking clozapine and two cases in those taking risperidone.Besides,three cases of myocarditis have been described only in subjects taking clozapine.[104]A postmortem diagnosis of myocarditis has also been described by Vang,et al.[8]This study included two case reports relating to the death of two young men,both who took olanzapine at therapeutic doses,who died suddenly.In both cases,an autopsy,histological and toxicological tests were carried out,which made it possible to make diagnoses of death of eosinophilic myocarditis.Another epidemiological study carried out using a database on autopsy data of all deaths occurring over a 26-year period(1984–2009) in adults receiving care in one large psychiatric hospital in New York,revealed the presence of twenty-two deaths from cardiovascular disease on one hundred cases of sudden death.The twenty-two deaths from cardiovascular death were divided as follows:fifteen deaths due to acute coronary syndrome,two deaths due to heart failure,two deaths due to aortic dissection,two deaths due to myocarditis,and one death due to commotio cordis.[103]Also,Ifteni,et al.[106]used a register of autopsy data from Maryland hospital databases from 1989 to 2013.This study included a cohort of 7,198 schizophrenic patients hospitalized in psychiatric facilities.Of these,fifty-seven patients died of sudden death during hospitalization and fifty-one patients underwent autopsy.On autopsy,62.8% of deaths were attributed to cardiovascular causes,such as myocardial infarction (52.9%),myocarditis(5.9%),and dilated cardiomyopathy.

However,it should be noted that no studies have analyzed the correlation between antipsychoticinduced cardiac death and oxidative stress in humans.In this regard,numerous preclinical studies previously exposed have highlighted the link between cardiac damage induced by oxidative stress/inflammation and antipsychotics.Concerning this,numerous molecules have been analyzed at the murine level;the alterations highlighted in the various studies conducted included an increase in TNF-α,an increase in catecholaminergic tone,an increase in the ROS and nitrate pathways,the presence of DNA degradation products,and lipid peroxidation,as well as alteration of endogenous antioxidant systems.

Specifically,animal models of myocarditis associated with the use of clozapine have shown an increase in TNF-α and free radicals,effects that were reduced with the use of propranolol,suggesting that the increase in catecholaminergic tone could mediate the inflammatory increase and oxidative stress in this pathology.[64]The scarcity of postmortem studies suggests the need for research in this sense,to be able to highlight whether oxidative stress can at least partially mediate cardiotoxicity due to antipsychotics also in human subjects.In this sense,the increase in TNF-α can be assessed in humans through immunohistochemistry investigations on cardiac histological sections previously treated with anti-TNF-α.[57]Furthermore,an index of cardiac damage from oxidative stress is represented by the increase in the levels of malondialdehyde,an indicator of lipid peroxidation,and the reduced glutathione/oxidized glutathione ratio,both of which can be assessed in humans through biochemical analyzes,respectively of chromatographic and spectrophotometric type.[108,109]

In addition to this,to highlight the presence of a correlation between oxidative stress and heart disease induced by antipsychotics,it would be useful to carry out immunohistochemical investigations aimed at assessing the presence of oxidative stress markers,such as inducible NOS,8-OHdG,NOX2,and finally the pathways of apoptotic death by TUNEL assay.[57]

CONCLUSIONS

Cardiotoxicity of atypical antipsychotics represents a major concern in clinical practice due to its large use in mental disorders.Major cardiovascular adverse events and sudden unexpected deaths are reported,but the mechanism of myocardial injury is not completely known.An increase in myocardial oxidative stress and inflammatory cytokines may play an important role in cellular death and DNA damage.Post-mortem examination is still crucial for research and must be seen as an opportunity for early detection of patients at risk for an unexpected death,and discovery of preventive measures.[110,111]Post-mortem studies carried out show increased cardiac death in subjects taking antipsychotics compared to the general population,reporting cases of myocarditis,cardiomyopathy,and sudden cardiac death.However,the pathogenesis of cardiac toxicity induced by these molecules is still unclear.A potential role of oxidative stress in cardiotoxicity caused by antipsychotics has been proposed in numerous preclinical studies,but post-mortem data from subjects taking atypical antipsychotics during life is extremely lacking.It would be desirable to carry out biochemical and immunohistochemical investigations on cardiac tissue of subjects who died of cardiac death related to antipsychotics,to verify whether oxidative stress can at least partially mediate the cardiotoxicity associated with the use of these molecules.If the mechanism of cardiac toxicity of antipsychotics is clarified in the future clinicians will be able to better establish the dose and length of treatment improving mental disease without impacting the physical health of the patients reducing mortality.[112–114]

ACKNOWLEDGMENTS

All authors had no conflicts of interest to disclose.